21... e6g4  22. c3e2 This move is refuted by Caruana's excellent reply. Both 22.Rc1 and 22.Rde1 keep the advantage. 22... f7f5 There is an accumulation of black pieces in the g-file, but interestingly this isn't bad. With this move, Black takes advantage of the strength of the bishops and the support of the knight on g7 to break White's center. 23. e4f5  23... g7f5 The best capture. Excellent calculation by Caruana, since he had to foresee what to do against White's next move.